There are numerous circumstances where contactless measurement of a resistance, from a remote measurement position across a gap of material (or air) from the resistance, is desirable. One example is measuring a thermistor resistance buried in a completely sealed device (e.g., a Li-ion battery pack). Contactless measurement (also referred to herein as non-contact measurement) of this resistance can provide information (correlated to temperature) needed for operational qualification and protection of the remote system. Numerous other applications employ thermistors that are not practically accessible through contacts, e.g., fluid temperature measurements in automotive applications, and rotating machinery such as motor windings.
Another example is resistance measurement for configuration control. If a resistor buried within a product is measured by an external contactless system, the measurement result can provide an indication of product configuration. For example, if a resistor embedded in a high volume product has resistance indicative of unique information such as lot code, authentication, expiration date, or other parametric information (such number of battery cells, container size, lot calibration information), then measurement of that resistance identifies the parameter(s).
There are other situations where contact measurements of resistance are possible, but problematic. One example is measuring the resistance of medical fluids. For instance, the resistance of a blood/reagent mixture (e.g., blood/glucose mixture) can be correlated to useful information (e.g., blood/glucose level) about the blood. The resistance measurement is conventionally performed by depositing the mixture on a test strip that is then inserted into a meter via a connector. The meter uses current sources and voltage measurements to determine the resistance of the blood/reagent mixture. However, after enough test cycles, the connector is prone to contamination and eventual failure. Significant material and process costs are required in order to make the connector interface between test strip and meter connector interface sufficiently robust to ameliorate the contamination/failure problem. Cost-effective contactless measurement of the blood/reagent mixture resistance could beneficially eliminate the need for the connector interface.
Although there are known techniques for making contactless voltage measurements, there is not currently available a technique to implement contactless resistance measurements, much less to do so in a simple and cost-effective manner.
It is desirable in view of the foregoing to provide for simple and cost-effective contactless measurement of resistance.